Why babies moan in sleep?

Babies may moan in their sleep due to various reasons, including the normal sleep cycle, where they experience active sleep or REM sleep, during which they may make noises. It can also be a way for them to express discomfort, such as gas or teething pain. Additionally, some moaning can be a response to dreams or simply a reflection of their developing nervous system. Overall, it's usually a normal part of sleep behavior in infants.